Propylene polymers that are random copolymers of propylene and 1-butene are used in films, sheets and the like because of their excellent properties such as heat resistance, transparency and scratch resistance.
Such propylene polymers are conventionally produced with solid titanium catalysts or metallocene catalysts including an alkylaluminoxane and a metallocene compound such as of zirconium or hafnium.
The conventional propylene polymers produced in the above manner, for example, those propylene polymers produced with solid titanium catalysts generally have a broad molecular weight distribution, and thus articles of the polymers such as films exhibit stickiness. While metallocene-catalyzed propylene polymers have a narrow molecular weight distribution, their heat resistance and heat sealing properties are not always satisfactory.
Due to their molecular structures, propylene polymers exhibit poor adhesion with respect to certain materials such as metals and polar resins. It is therefore necessary to treat the surface of propylene polymers by a method such as flame treatment, corona treatment or primer treatment so that the polymers and such materials as metals can form composite stacks.
To obtain improvements in the properties of polyolefins such as propylene polymers, graft-modified polyolefins are used which are obtained by the graft modification of polyolefins with polar monomers such as maleic acid.
JP-A-H09-278956 discloses a method for producing maleic anhydride-modified polyolefins characterized in that a mixture including 100 parts by weight of a polyolefin, 0.1 to 20 parts by weight of maleic anhydride and 0.01 to 20 parts by weight of an organic peroxide having a one-minute half-life decomposition temperature of 150 to 200° C. is melt-kneaded in a twin-screw kneading extruder to modify the polymer. However, maleic anhydride-modified polyolefins obtained by this production method have a strong odor. Further, dispersing the modified polyolefins into aqueous media results in white turbidity.
Furthermore, primers prepared by dissolving the modified propylene.α-olefin copolymers into solvents such as toluene contain components which are insoluble in the solvents, and this fact causes a decrease in the yield of the primers.